This invention relates to the dehydrogenation of C2-C3 alkyl aromatic compounds to produce vinyl aromatics and, more particularly, to the catalytic dehydrogenation of such alkyl aromatic compounds in a tubular reactor incorporating an elongated spiral mixing section.
Various vinyl aromatic compounds can be prepared by the catalytic dehydrogenation of corresponding C2 or C3 alkyl aromatic compounds. Such reactions include the catalytic dehydration of monoalkyl or polyalkyl aromatics, such as ethylene and diethylbenzene or the dehydrogenation of alkyl substituted polynuclear aromatic compounds, such as ethylnaphthalene. Perhaps the mostly widely used dehydrogenation process involves the dehydrogenation of ethylbenzene with the production of styrene. The catalytic dehydrogenation of ethylbenzene is typically carried out at temperatures within the range of about 540-660xc2x0 C. under near atmospheric or even subatmospheric pressure conditions. Typically, an ethylbenzene steam feed having a steam to ethylbenzene mole ratio of perhaps 7 or 8 or even higher is passed over a dehydrogenation catalyst such as iron oxide in an adiabatic dehydrogenation reactor. The dehydrogenation reactor may be of various configurations including a radial flow reactor such as disclosed in U.S. Pat. No. 5,358,698 to Butler et al or a linear or tubular reactor such as disclosed in U.S. Pat. No. 4,287,375 and No. 4,549,032, both to Moeller et al. As disclosed, for example in the aforementioned ""032 patent to Moeller et al, an iron-oxide-based dehydrogenation catalyst is employed in a tubular reactor containing a plurality of reaction tubes which are heated by a hot molten salt bath.
Yet another reactor system for the catalytic dehydrogenation of ethylbenzene to produce styrene is disclosed in U.S. Pat. No. 6,096,937 to Butler et al. In the Butler et al system, a reactor system comprises a furnace structure which incorporates a plurality of internal reactor tubes which contain a dehydrogenation catalyst and which operate in an ascending heat mode. Here, the reactor system incorporates gas-fired heaters which heat the interior of the furnace to a temperature suitable for dehydrogenation to bring the temperature within the reactor tubes to the desired level by the application of heat which varies along the length of the tubes.
Analogous dehydrogenation reactions can be carried out employing C3 alkyl aromatic compounds. Thus, n-propyl benzene can be dehydrogenated to produce beta methyl styrene, and cumene can be dehydrogenated to produce alpha methyl styrene. Other reactions include the dehydrogenation of ethyl toluene to produce vinyl toluene and the dehydrogenation of diethylbenzene to produce divinyl benzene.
In accordance with the present invention, there is provided a process for the dehydrogenation of a C2 or C3 alkyl aromatic compound to a corresponding vinyl aromatic compound in a tubular reactor incorporating a spiral flow path. In a preferred embodiment of the invention, there is provided a process for the production of divinyl benzene by the catalytic dehydrogenation of diethylbenzene. In carrying out this embodiment of the invention, a feedstock containing diethylbenzene and steam is supplied into the inlet of a tubular reactor containing a dehydrogenation catalyst. The tubular reactor is operated under temperature conditions effective to cause the dehydrogenation of diethylbenzene with the attendant production of divinyl benzene in the presence of the dehydrogenation catalyst. Within the reactor, the feedstock flows through at least a portion of the reactor along a spiral flow path extending longitudinally of the reactor. The resulting divinyl benzene product is then recovered from a downstream or outlet section of the reactor. Preferably, the spiral flow path through which the feedstock is passed is located at least adjacent the inlet side of the reactor, and at least a portion of the spiral flow path contains a particulate dehydrogenation catalyst.
In a further embodiment of the invention, a spiral flow path extends throughout a major portion of the elongated tubular reactor and at least a substantial portion of the spiral flow path contains a particulate dehydrogenation catalyst. Preferably, the steam to diethyl benzene mole ratio of the feedstock is about 16 or less and more preferably within the range of about 8-13. The invention is particularly applicable to a variable heat (non-adiabatic) process in which heat is applied externally to the tubular reactor to provide an amount of heat which varies along the length of the tubular reactor.
In a further aspect of the invention, a feedstock containing diethylbenzene and steam is supplied into a plurality of tubular reactors located within the interior of a dehydrogenation reactor vessel. The tubular reactors are arranged in a parallel relationship relative to one another in which the tubular reactors are spaced laterally from one another and are spaced from the interior wall of the reaction vessel. The tubular reactors each have a mixing stage comprising a longitudinally-extending helical baffle providing a spiral flow path for mixing of the diethylbenzene and steam within the reactor. The interior of the reaction vessel is heated by a gas-fired or other suitable heating system in order to provide a heating zone externally of the tubular reactor to provide an amount of heat which varies along the lengths of the tubular reactors. The supplied mixture of diethylbenzene and steam flows through the parallel tubular reactors into contact with a particulate dehydrogenation catalyst in the reactor under temperature conditions, resulting from the externally-applied heat, which are effective to cause the dehydrogenation of diethylbenzene to divinyl benzene in the presence of the dehydrogenation catalyst. Subsequent to the dehydrogenation reaction, the divinyl benzene product is recovered from the tubular reactors through outlets located downstream of the dehydrogenation catalyst.
In a further aspect of the invention, there is provided a reaction system for the catalytic reaction of a plurality of reactants in a feed stream. The reaction system comprises a plurality of parallel, elongated, tubular reactors having inlet and outlet sides. An inlet manifold is connected to the tubular reactors in order to supply a mixture of reactants to the inlet sides of the tubular reactors. The reactors incorporate a mixing section adjacent the inlet sides thereof, each reactor comprising at least one static baffle in an elongated helical configuration comprising a spiral flow path. A reaction section in each of the tubular reactors is located downstream of the initial mixing section and comprises a bed of catalyst particles. An outlet manifold is connected to the outlet side of the tubular reactors and is effective to supply reaction product from the tubular reactors to a suitable recovery system.